1. Field of the Invention
The present invention relates to a digital camera, lens unit, and camera system having the same. More particularly, the present invention relates to a digital camera, lens unit, and camera system having the same, which is suitable in view of reliable transmission of image signals by appropriately constructing contacts for electrical connection in an interchangeable unit for use with a camera body.
2. Description Related to the Prior Art
A digital still camera is widely used, and includes an image pickup device or CCD for photographing an image to store the image to a data storage, such as an internal memory, memory card or the like. Various cameras are known, including a unified type in which a camera body includes a photographing lens, and a lens interchangeable type in which the photographing lens is removably mounted on the camera body.
JP-A 2001-116972 discloses a conventional construction of a lens interchangeable type of the digital still camera, in which parts in a camera for with silver halide photo films are utilized without structural changes. The image pickup device or CCD is incorporated in the camera body in place of a photo film, to pick up and record an image by use of a storage. An interchangeable lens for the digital still camera is basically the same as that for a photographic camera.
Owing to technical development in the field of imaging, the image pickup device or CCD comes to have a gradually smaller size than before, and a greater number of pixels. It is conceivable regarding the digital still camera that the CCD is contained in the interchangeable lens as a renewed structure of a lens changeable product, which is in place of utilizing easily available structures of cameras for use with silver halide photo films. According to the conception, no optical connection is required between the interchangeable lens and the camera body. The interchangeable lens can be connected with the camera body only electrically. This is advantageous in possibility of simplifying the structure.
In a system with the interchangeable lens, a lens unit is combined with the camera body of the digital still camera. It is necessary to transmit control signals and supply power from the camera body to the lens unit. To this end, the lens unit is provided with lens connection contacts for use with camera contacts which the camera body includes. When the lens unit is set on the camera body, those are electrically interconnected by the touch between the lens connection contacts and the camera contacts.
So far, flexible wiring boards have been widely used for connection between a circuit board in the lens unit and the lens connection contacts. However, several attempts are made for saving a mechanical space inside the lens unit because of high density in mounting of relevant parts. For example, JP-A 2001-116972 discloses arrangement of the lens connection contacts, which includes the circuit board, the lens connection contacts and wiring. The circuit board for lens control is secured to the inside of the lens unit. The lens connection contacts are secured to a rear end of a lens mount. The wiring connects the lens connection contacts to the circuit board electrically. An opening is formed in the circuit board for coming the lines from the lens connection contacts. Ends of the lines of the lens connection contacts extending through the opening are connected with the wiring, so that a space for the wiring can be saved. JP-A 2003-302563 discloses arrangement of the lens connection contacts, which includes plural pins of the lens connection contacts, a flexible wiring board as the circuit board, and a supporting body secured on the lens mount for supporting the pins and the flexible wiring board. The pins of the lens connection contacts are constituted by compressed springs compressed in a radial direction of the lens mount. Also, there is a digital still camera α 3700i (trade name) manufactured and sold by Minolta Corporation. This includes the circuit board of a rigid form and having a plurality of the lens connection contacts mounted thereon. The circuit board is secured to the rear end of the lens mount. A part mounted circuit board or camera circuit board is connected to the circuit board by wiring of the flexible wiring board.
It is however impossible to save an internal mechanical space according to the structures of JP-A 2001-116972 and JP-A 2003-302563 and the digital still camera α 3700i (trade name). In the digital still camera of JP-A 2001-116972 and JP-A 2003-302563, the lens connection contacts for use with the camera contacts has a shortcoming in the considerable large number of the parts of the lens unit, because one member or part of contact is required for each of the lens connection contacts. According to the digital still camera α 3700i (trade name), the image pickup device or CCD extends between the circuit board and the part mounted circuit board or camera circuit board. A value of impedance of the flexible wiring board creates a low level of a communication speed as a bottle neck despite requirement of a high speed of the communication speed in connection with the part mounted circuit board or camera circuit board. The disposition of the CCD in the lens unit further raises the density of mounting the parts. Data must be transmitted to the camera body at a high level of the communication speed. It is extremely difficult to reduce a space in the lens unit in the case of the lens connection contacts and the camera contacts of the above. No sufficient highness of the communication speed can be obtained in connection with the camera body.
Also, U.S. Pat. No. 6,845,218 (corresponding to JP-A 2004-361898), JP-A 11-169347 and JP-A 2004-341265 disclose known cameras having the interchangeable lens and capable of detecting a loaded state of the interchangeable lens. However, it is still impossible to detect an incompletely loaded state. In the retention for use with bayonet lugs, it is likely that the interchangeable lens may not be rotated, or may be rotated only at a point short of the rotational position for the fully loaded state. A problem arises that a user will not be aware of the incomplete of the interchangeable lens. Image pickup cannot be made. Also, he or she erroneously determines occurrence of failure because of lack of image signals transmitted to the camera body. In particular, the problem is serious for a system with the interchangeable lens containing the image pickup device or CCD. No image data will be sent to the camera body if no setting in the fully loaded state is ensured, because the lens connection contacts and the camera contacts must interconnect for data transmission from the CCD to the camera body.